The present invention relates to a method of controlling the drive of computer-controlled transporting device, in particular crane facilities with lifting winches and at least one mast supported on a moving frame on which are mounted shelf operator devices provided with load-carrying means and a lifting platform, and including a current control circuit, a drive control circuit with a speed control circuit and a position control circuit.
U.S. Pat. No. 5,239,248 discloses a control method in which the above mentioned control circuits are used and according to which the behavior of the apparatus is taken into account from an available data tree of a state and disruption monitor-regulator module using the already available measurement and setting values. Apart from the fact that only a limited number of measurement and setting values are processed, the known method deals with a pure position control.
The above-mentioned shelf operator devices or material handling equipment which, e.g., are disclosed in German Patent No. 3,803,626, are used, e.g., in logistic systems, which include as an important component a high-lift carrier, to perform completely automatically or manually a transportation task, i.e., a transfer of a unit load from a storage site to a stockyard and from their to a discharge site. The range of stored goods extends from a packing with a weight of several kilograms to heavy rolls with a weight of about 40 tons, e.g., of wound-up metal bands. The site height and the dependent thereon height of a shelf operator device is in a range from about 6 m to 45 m. The site dimensions are accessible by a freely movable or displaceable on rails shelf operator device by its travelling mechanism in the horizontal x-direction, by its lifting mechanism including a vertically displaceable lift drive on the upright mast for a lift platform, in the vertical y-direction, and by load-carrying means drive in the z-direction. High straight masts, on which the above-mentioned large load move up and down from time to time, are flexible, extremely oscillatory systems with variable dynamic characteristic which can be excited, e.g., by motive acceleration and deceleration, roadway bumps, braking and control action.
In view of the costs, power consumption and operational dependability aspect a technico-economical optimization of shelf operator devices and crane facilities, in particular of the travel and lift drives, including their controls, assumes a large importance because those, together with pure mechanical parameters, substantially affect the dynamic behavior. The object of the known control and regulation strategies is to minimize the time of loading and unloading of loads (transport units and/or goods) and to reduce the dynamic loading of structural and mechanical components of the shelf operator device or a crane facility. It is to be noted here that the normal times of the lift and travel drives include the pure movement times and the slow-down times resulting, e.g., from acceleration or braking-caused vibrations of the mast or frame and/or carrying cables. When the mast oscillates, the transfer of the load from the lift platform to a shelf cannot be carried out because of a danger of a possible damage. Rather, one should wait until the amplitude is reduced to a certain limit magnitude. From this, it can be concluded that the dynamic behavior significantly influences the throughput and, thus, the economic efficiency of a logistic system which includes a high lift carrier.
In view of the above, a throughput increase by high accelerations and speeds is excluded because the resulting therefrom large vibration amplitudes and long slow-down times are inevitable. As a result, the total time increases despite the reduction of the movement time. As a starting point for solving the existing optimization problem with contradictory objectives, one turns to drive controllers because due to the logistic definition of the problem and due to the required dimensioning, which is based on the rigidity requirements, the geometrical shape of a shelf operator device can be changed only with a great difficulty. To this end, servomotors with servo-drive amplifier, D.C. motors with power converters, and three-phase asynchronous motors with frequency converters are used as drive controllers for lift and travel drives having interface for different speed-changeable electrical drive. The interfaces limit the controllers hierarchically downward. The upward interface is obtained by the device control which provides the controller with final points of the travel movement and which is responsible for safety functions, stop functions, coordination tasks, error diagnosis, communication with the position maintaining computer, ets. An external interface connects a controller with a path measurement system which supplies the controller with an absolute or indirect measurement of an instantaneous position of the apparatus. These measurement systems are usually formed as form-locking skid-free systems or as frictionally engaged systems, which are susceptible to sliding, with a following multiple precision positioning.
Further, the so-called "3-point position control" and a "cascade control", which are formed of three different, cascade-connected control circuits, with the current control circuit as an inner circuit, and the speed control and the position control circuits as outer circuits, relate to the state-of-the art control concepts. In these control concepts, the "3-point position control," strictly speaking, is not a control at all, rather it presents a path-dependent speed control, resulting in a multi-stage deceleration process with a loss of time. Because no continuous adjustment between an actual position value and the set value takes place, the accumulated position deviations are compensated only at the end of the deceleration process during a creeping movement with a reduced speed. Thus, the multi-stage positioning brings with it multiple speed changes and thereby changes of acceleration and deceleration which stimulate the oscillation of the mast or cables of the apparatus. Contrary to this, the cascade control is characterized by a continuous comparison of the actual position value and the set position value, with the active compensation of the position deviation by adaptation of the set speed values. This concept results in few starting points for stimulating oscillations.
For minimizing the oscillation, with both control concepts, a passive process is used in which timed changes of the acceleration, and, thereby, the accompanying jolts, are limited by setting forth a suitable command variable. Thereby, a transition is made from a discrete acceleration change to a linearly increasing or sinusoidal rounding. The drawback of this oscillation reduction consists in that with rounding with retaining of maximal acceleration values, the mean acceleration decreases which results in inevitable time losses.